Previously, self-contained gas springs have been constructed with an actuating rod connected to a piston slidably received in a cylinder having a chamber which is precharged at a predetermined pressure, such as 2,000 psi, with an inert gas such as nitrogen. When the rod and piston are forced into the chamber, the gas therein is compressed to a maximum operating pressure which is usually in the range of about 3,000 to 5,000 psi, depending on the volume of the chamber and the effective area and stroke of the piston. In normal use, the pressure to which a self-contained gas spring is initially charged is not varied or changed. The spring is initially charged, relieved and recharged through a high pressure charging valve construction mounted in a filler block closing the rear end of the casing of the gas spring. In some applications the charging valve is operable to adjust the gas spring charging pressure by release of gas pressure from the spring chamber to ambient and then recharging through the valve to a new set pressure. Preferably the chamber port of the filler block is internally threaded to receive a flexible hose coupled to an external gas source, as well as for threadably mounting the gas spring on a suitable externally threaded support.
Examples of prior gas springs and systems are disclosed in U.S. Pat. Nos. 4,792,128; 4,838,527; 5,020,570 and 5,303,906 assigned to Diebolt International, Inc., the assignee of record herein, and which are incorporated herein by reference. In particular, the gas spring charging valve filler block construction disclosed and claimed in conjunction with the embodiment illustrated in FIGS. 6-8 of the '906 patent has been used successfully commercially and has proved advantageous with respect to its relative simplicity of manufacture and assembly, and because it cannot be tampered with from outside the pressure vessel. The valve has no moving metal parts and merely uses an elastomeric O-ring as a movable one way check valve member and seal.
However, the valve is designed for charging of a gas spring one time only. In addition to this limitation, in commercial manufacture and use certain problems have been discovered relative to the construction and operation of this fill valve. Although the O-ring was specified with a preferred durometer of 70, experience has shown that a 90 durometer hardness was needed in the high pressure range of operation of the gas spring to resist extrusion of the elastomeric material of the O-ring through the small diameter charging hole 122 of the central modular head 114 of the valve construction. Even increasing the durometer to 94 has been found not to prevent such O-ring failure in certain applications. Moreover, use of the harder O-ring material limits the capability of the O-ring to seal at lower pressures, e.g., 200 to 400 psi, because of its reduced capability to fill in imperfections in the O-ring sealing surfaces 116 and 118 of this valve construction.
It has also been found that in the manufacturing process of the '906 filler block it is difficult to control or monitor the surface finish for these O-ring seating surfaces 116 and 118 in the rear head 114. Also, to prevent damage to the O-ring the lateral port 122 entering at the bottom of the V-shaped recess or groove 120 should be of relatively small diameter, preferably about 0.015 inches. Accordingly, the size of the drill required for drilling this charging hole is fragile and subject to breakage, which is difficult to detect in the manufacturing process. The drilling process also requires removal of burrs after drilling. Geometrically, the localized radial entry of this small diameter lateral port 122 at the bottom of the V-shaped groove 120 relative to the overlying O-ring 124 with its 360.degree. sealing surfaces 116 and 118 inherently contributes to unequal pressure distribution and hence sealing forces which can contribute to leakage problems.